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Tree biomass and it's allocation pattern may respond to the environmental conditions and are quite important for understanding the global carbon cycling, climate change, and forest management. However, how stand characteristics (e.g. tree age, density) and environmental factor (e.g. climate, site conditions, and soil chemistry) influence the biomass and biomass allocation in southwest of China has not been well investigated. We analyzed 318 field measurements of forest biomass in this region, which 62 sites were obtained from our field measurements and the others from the national forest inventory. The results showed that the average above-ground biomass (AGB) and below-ground biomass (BGB) were 134 Mg/ha and 28 Mg/ha, respectively. The root/shoot biomass ratio (R/S) ranged between 0.06 and 0.81, with an average of 0.22. Forest stand characteristics explained 43% and 21% of the variation in AGB and BGB, respectively, while climate only explained 2–4%, reflecting the strong effect of forest features on biomass. However, only 5% of the R/S ratio was explained by climate, soil chemistry, and stand characteristics, suggesting that these factors had no significant effect on biomass allocation. In addition, the scaling exponents between AGB and BGB did not differ significantly from 1, and did not vary with mean annual temperature, mean annual precipitation, longitude, latitude, altitude, soil pH, soil total nitrogen concentration, and stand age, but did vary with soil total phosphorus concentration, stand density, and forest type. Our findings suggest that stand characteristics have a marked impact on forest biomass, and root biomass scales isometrically with above-ground biomass in southwest China. [ABSTRACT FROM AUTHOR]

Million-hectare plantations of Cyclobalanopsis glauca were planted in southwest China to restore the degraded vegetation. Although many studies of these plantations have been conducted, from the genetic scale to regional scales, the role of stand age in regional carbon (C) cycling remains unclear. In this study, we examined the biomass and C storage of the main ecosystem components in five C. glauca plantation stands in Guangxi Province, southwest China, that ranged in age from 8 to 70 years. The ecosystem and tree biomass increased with increasing stand age. On average, the highest C concentration was found in tree branches, whereas the lowest C concentration was found in the underground parts of herb. C concentration in trees, shrubs, herbs, and litter were age-dependent. C storage in C. glauca plant biomass in stands aged 8, 20, 40, 50, and 70 years was 40.45, 78.25, 90.41, 94.46, and 114.69 Mg ha −1 , respectively. Soil organic C (SOC) storage in the top 1 m of soil in plantations aged 8, 20, 40, 50, and 70 years was 70.38, 90.84, 84.39, 47.91, and 107.99 Mg ha −1 , respectively, with SOC concentration decreasing with increasing soil depth. Total C storage in the plantation ecosystem averaged 110.83, 169.09, 174.80, 142.37, and 222.68 Mg ha −1 in the 8-, 20-, 40-, 50-, and 70-year-old plantations, respectively, with most of the C storage in the aboveground biomass and soil rather than in the belowground biomass. Our results suggest that successional development as temporal factor influencing C storage in plantations are important considerations for fully realizing the ecological value of the C. glauca plantations in southwest China. [ABSTRACT FROM AUTHOR]

• Tree size was the most important driver of tree survival. • Abiotic variables and neighborhood effects were of secondary importance. • Importance of factors differed among guilds and species. • Relative importance of intrinsic and extrinsic factors must be considered. Understanding tree mortality and the underlying driving mechanisms is essential for understanding forest dynamics and tree species coexistence. Based on survival data from two censuses of a large (25-ha) fully mapped subtropical karst forest plot, the present study quantified the simultaneous effects of tree size, soil, topography, and neighborhoods on tree mortality at three levels (community, guild, and species). Our study suggested that tree size, biotic neighborhood, and abiotic factors influenced tree survival, but the relative importance of these mechanisms for tree mortality differed greatly among species guilds. Of the variables tested, tree size was the most important driver of tree survival, and had a strong negative relationship with tree mortality, while abiotic variables and neighborhood effects were of secondary importance. Regarding abiotic factors, both soil and topography affected tree survival. Abiotic factors generally influenced the survival of common trees, smaller individuals, and slow growing, shade-tolerant understory species. Regarding biotic factors, the biotic neighborhood effects may be irrelevant for tree survival under these conditions, as indicated by the results of both conspecific neighbor density and heterospecific neighbor density analyses. These results suggested that it is necessary to simultaneously consider the relative importance of intrinsic (tree size) and extrinsic (biotic and abiotic) factors on forest dynamics to better understand, conserve, and manage subtropical karst forests. [ABSTRACT FROM AUTHOR]

• Soil nematode richness is relatively low on inshore islands. • Large island maintains high soil nematode abundance and diversity. • Edaphic and climatic-geographical factors drive variations in soil nematode compositions. Factors that influence the composition and diversity of soil nematode communities on oceanic islands are poorly understood. In this study, we evaluated the soil nematode communities and associated biotic and abiotic factors on five oceanic islands in the north of the South China Sea. We detected 38 nematode genera and found that bacterivores and fungivores were the dominant trophic groups, representing 54.2–70.4% and 15.1–35.3%, respectively, of total soil nematode abundance. The abundances of total soil nematodes and of all trophic groups, maturity, structure indices and nematode diversity were positively correlated with island latitude and area, and were negatively correlated with soil total K and annual temperature. In addition, the abundances of total soil nematodes, bacterivores, herbivores and nematode dominance index were positively associated with soil available K. The abundances of total soil nematodes, fungivores, herbivores, predators and omnivores, maturity, structure, Shannon diversity indices were positively related to soil moisture. Variation partitioning analysis showed that the combination of soil properties and climatic-geographical factors explained more of the variation (26.8–61.5%). The results suggest that larger island can maintain greater nematode diversity than smaller islands due to the greater diversity of habitats on larger island. The key climatic-geographical and edaphic factors affecting soil nematode communities were latitude, annual temperature, soil moisture and total K, respectively [ABSTRACT FROM AUTHOR]

• Fungi and woody plant diversity showed inconsistent patterns among habitat types. • The major fungal functional groups showed similar richness patterns among habitats. • Woody plant alpha diversity was an important indicator of saprotrophic and pathogenic fungi. • Relationships between fungal and woody plant communities depended on habitat types. The diversity patterns of macroorganisms (i.e., plants) among different habitats have been well documented, however, those of microorganisms (i.e., fungi) as well as the relationships between them are still unclear. Here, we tested whether and to what degree fungal diversity was related to habitat types and compared diversity patterns of woody plants and soil fungi. We carried out field investigations on soil fungi in different habitat types (i.e., valleys, foothills, hillsides, and hilltops) in a 25-ha karst broadleaf forest in Southwest China. The tree richness, Shannon index, and Simpson index significantly increased from valleys to hilltops. While the soil fungal N 1 diversity (the exponential Shannon index) marginally increased toward valleys, fungal N 0 (richness) and N 2 (the inverse Simpson index) diversity exhibited significantly reduced and increased patterns, respectively, from valleys to hilltops. The major fungal functional groups (i.e., EcM, AM, saprotrophic, and pathogenic fungi) showed similar increasing richness patterns in valleys. Moreover, woody plant alpha diversity was an important indicator of fungal functional groups except for EcM and AM fungi. In addition, woody plants increased in species turnover rate (β SIM) from valleys to hilltops, while fungal species had a concave distribution. The patterns of nestedness (β SNE) for tree species decreased from valleys to hilltops, while the opposite was true for soil fungal species. Our findings indicated that the diversity patterns of woody plants and fungi were inconsistent among habitat types, and the relationships between fungal and woody plant communities depended on habitat types in the karst forest. [ABSTRACT FROM AUTHOR]

• Soil bacterial and fungal richness and diversity had spatial patterns. • Soil pH and available phosphorus were the key factors for soil bacteria. • Plant diversity and density were the key driving factors for soil fungi. • Slope was the most important factor for microbial dynamics in the karst forest. Soil microorganisms regulate ecosystem function and aboveground community dynamics in terrestrial ecosystems. However, our current understanding of the drivers of soil microbial diversity lags our understanding of macroorganisms. Here, we used Illumina sequencing of 16S and ITS rRNA genes to explore which factor(s) controlled soil microbial (i.e., bacteria and fungi) richness and diversity in a 25-ha karst broadleaf forest in Southwest China. Across the plot, all bacterial and fungal richness (number of OTUs) and diversity indices (Shannon diversity and phylogenetic diversity) showed strong spatial autocorrelations. Soil microbial richness and diversity indices displayed a unimodal pattern from south to north in the karst forest, with peaks in the low and middle areas of the plot. Slope was found to be the best predictor of soil bacterial and fungal richness and diversity indices. Soil pH was negatively related with bacterial richness, and with bacterial and fungal phylogenetic diversity. Tree Shannon diversity and density together explained much of the variations in fungal OTUs and diversity indices. Spatial factors explained much less of the variation in soil microbial richness and diversity indices than the selected environmental variables, which indicated that habitat heterogeneity rather than dispersal limitation played an important role in soil microbial richness and diversity in the karst forest. In conclusion, slope was the major driver of the spatial distribution of soil microbial richness and diversity in the karst forest due to its effects on plant (i.e., tree Shannon diversity and tree density) and soil characteristics (i.e., soil pH and available phosphorus). [ABSTRACT FROM AUTHOR]

Knowledge of vegetation water depletion and the underlying mechanisms are essential for understanding eco-hydrological processes and fragile ecological environment protection. Based on a 2-year field experiments, this study investigated the transpiration and its influencing factors for three karstic climax forest communities located in the depression (DeC), mid-slope (MsC) and summit (SuC) of a typical karst hill in southwestern China. The meteorological factors, sap-flow, eddy covariance and soil moisture were measured. Results showed that the annual transpiration for SuC, MsC and DeC, were 701.0 mm yr−1, 626.4 mm yr−1 and 663.1 mm yr−1, respectively. The daily transpiration was significantly correlated to the air temperature (r > 0.6, P < 0.05), solar radiation (r > 0.8, P < 0.05) and water vapor pressure deficit (r > 0.3, P < 0.05), but showed no strong relationship with the shallow layer water content (SLWC, 0–40 cm). Moreover, the transpiration of the three communities generally maintained high rate (e.g., > 4.0 mm d−1 in the growing seasons), even when the SLWC dropped to about 0.15 cm3 cm−3 in the SuC during dry spells. Overall, 77.6%, 78.3% and 90.8% of the transpired water in the SuC, MsC and DeC respectively, came from the shallow layer. These suggested that the plants in this region could uptake water from deep layers when the SLWC is limited, and implied that the climax forest communities were generally not limited by water, at least in normal years. • Transpiration of karstic climax forest (KCF) was mainly affected by meteorology. • Most of the water transpired by KCF came from the shallow layer (0–40 cm). • KCF also maintain high transpiration even during dry spells. • KCF should use deeper sources when water in shallow layer is limited. [ABSTRACT FROM AUTHOR]

Soil carbon (C) sequestration through cropland conversion has been regarded as a major strategy to absorb atmospheric CO 2 and thus mitigate global warming, but much uncertainty still exists in terms of restoration strategies. In this study, soil C and nitrogen (N) were measured 13 years after cropland conversion in a karst area, southwest China. Four restoration strategies were included, i.e., (i) restoration with an economic tree species Toona sinensis (TS), (ii) restoration with Guimu-1 hybrid elephant grass (GG), (iii) restoration with a combination of Zenia insignis and Guimu-1 hybrid elephant grass (ZG), and iv) spontaneous regeneration (SR). Cropland under maize-soybean rotation (CR) was used as reference and the space-for-time substitution approach was adopted to evaluate soil C and N stock (0–15 cm) change. Soil C stocks in TS and SR were elevated by 40% and 50%, respectively, relative to CR, while those in GG and ZG were not significantly changed. Soil N stocks in GG were not significantly changed, but stocks in TS, ZG and SR were enhanced by 130%, 81% and 117%, respectively, relative to CR. Significant correlation was found between soil C and N stock changes with rate of relative N stock change greater than that of C stock change. Similar to soil N stock, nitrate concentration, net nitrification rate and δ 15 N values in TS, ZG and SR were greater than those in GG or CR. Stepwise multiple linear regression indicated that exchangeable calcium was the soil variable mainly responsible for the dynamics of both soil C and N. Our results indicate that plantation with economic tree species and spontaneous regeneration are likely equally effective in soil C sequestration. [ABSTRACT FROM AUTHOR]

Highlights: [•] Soil nematodes were affected more by fertilization and irrigation than by cutting. [•] Fertilization had both positive and negative effects on soil nematode community. [•] A hypothetical trade-off between the positive and negative effects was proposed. [•] Additional water applied in irrigation was detrimental to soil nematodes. [•] Soil health benefits from an optimal combination of fertilization, irrigation and cutting. [Copyright &y& Elsevier]

Soil microorganisms are important for plant nutrients and health. However, our understanding of soil microbial communities in the rhziosphere and bulk soils as plant succession stages increased in the Karst area remains unclear. Here, we evaluated how the bacterial and fungal communities of rhizosphere and bulk soils respond to different vegetation succession stages: grassland (GR), shrubland (SH), secondary forest (SF), and primary forest (PF). The abundance and composition of bacteria and fungi were determined by qPCR and MiSeq high-throughput sequencing methods, respectively. The results showed that the abundance and diversity in rhizosphere and bulk soils were diminished among vegetation succession stages. We found that SOC led to high microbial abundance in GR and SH during the period of primary succession stages, while AP potentially led to low abundance of microbes in the PF and SF of subsequent succession stages. Additionally, the OTUs shared by four succession stages (common OTUs) comprised approximately 87.61 ‐ 98.90% of the total relative abundance of bacteria and fungi in the rhizosphere and bulk soils, which indicated that the composition of fungi and bacteria in these environments were similar across different succession stages. pH might be an important driving factor involved in the similarity of bacterial and fungal compositions among different succession stages. However, the relative abundance of bacterial and fungal phyla across the four vegetation stages was different, and also determined by multiple soil properties. pH was the main factor determining bacterial community structure in rhizosphere soils, whereas SOC was the principal determinant of the same parameter for bacteria in bulk soils, and in both the rhizosphere and bulk soils for fungi. Overall, our results suggested that bacterial and fungal communities in the rhizosphere and bulk soils diminished with vegetation stages, which may provide evidence that mechanisms underlying the soil microbe-driven vegetation succession in the Karst area of southwest China. • The soil properties, other than the plant types and root effect, induced the changes of abundance and composition of bacteria and fungi in rhizosphere and bulk soils. • The SOC induced significant changes in the abundance of bacteria and fungi in the GR and SH in both rhizosphere and bulk soils of the primary succession stages. AP potentially lead to low abundance of microbes in the PF and SF in both rhizosphere and bulk soils of the later succession stages. • pH may be a key factor resulting in the diminished of bacteria and fungi composition and diversity across different succession stages. SOC might be an important factor influencing distribution patterns of the bacteria and fungi in rhizosphere and bulk soils. [ABSTRACT FROM AUTHOR]